Radio relaying system



P. C. MARCOU RADIO RELAYING SYSTEM ffy. 1 /0/007 /equency Pasana/f;

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March 9, 1954 P. c. MARcou 2,671,850

RADIO RELAYING SYSTEM Filed Feb. 4, 1952 4 sheets-sheet s Fay 4 Ffa! )&C. Maroo( March 9,A 1954 4 Sheets-Sheet 4 Filed Feb. 4, 1952 1n deh.,for' Patented Mar. 9, 1954 UNITED STATES TENT OFFICE Claims priority,application France February 7, 1951 (Cl. Z50-15) 3 Claims. 1

The present invention relates to a device for simultaneous reception andretransmission without reaction between the transmitter and the receiverwhich are placed near each other.

This invention relates generally to a radio relaying system and todevices of the so-called responder type which employ continuousmodulated carrier waves to convey the signals. It is also applied toapparatus of the kind which have to retransmit a pulsatory wave with adelay which is less than the duration of the pulses which compose thispulsatory wave, in which case the received and retransmitted pulseshave, in the time, a common portion.

The responder of the invention is not intended to form part of a chainof intermediate relaying stations placed at intervals between twoterminal stations. It is intended to receive a wave transmitted by agiven station and to return this wave, exactly on the same frequency, tothis station in order to produce a signalling action thereat.

Responders have the known disadvantage of giving rise to singing ofoscillations by reaction between the transmitter and the receiver.

In pulse modulated carrier wave systems, it is possible to use a singlewave-length on the to and fro sides of the responder station. Thetransmitter of the responder station is driven by the received pulsesand mutual interference is prevented by retransmitting the pulses aftera suitable small delay, the receiver being blocked for the period ofeach retransmitted pulse.

In continuous modulated carrier wave systems, various expediente havebeen proposed for preventing singing. Among these expedients are changeof carrier frequency in the responder station, employment of theso-called superregenerative circuit in which an amplifier having afeedback that would tend to permit or produce continuous oscillations isassociated with a quench oscillator which periodically checks there-amplifyng process and a method which consists in demodulating thesignals received, recording them on a recording medium and utilisingthem as modulation of a radio-frequency transmitter.

The disadvantage of the first solution is that, the return wave having afrequency different from the incoming wave, it cannot be used when it isdesired to produce a signalling action in a radioelectric station onlyin the case when the said station receiving from a responder a wavewhich has exactly the same carrier frequency as the wave transmitted bythis station. The disadvantage of the seconol solution is that it cannotoperate on a wide `frequency band and with a sub- CTI stantialretransmission power. Finally, the Adisadvantage of the third solutionis that the retransmitted frequency is fixed and is not driven by theincoming wave frequency.

One of the objects of the present invention is to provide aretransmitting device without coupling between the transmission and thereception, which device operates in the case in which the received waveis a continuous wave and utilises for the retransmission the samecarrier frequency as for the reception.

Another object of the invention is to provide a retransmitting devicewhich operates on a single frequency without coupling between thetransmission and the reception and renders possible a considerablediiference of level between the received signal and the retransmittedsignal.

Another object of the invention is to provide a retransmitting devicewhich is insensitive to the reflections of the retransmitted energy onneighbouring obstacles. Y

According to the main feature of the invention, the radio-frequencyreception and transmission amplifiers of the retransmitter are blockedand unblocked at the same cadence and in such a manner that the blockingtimes of one correspond substantially to the unblocking times of theother. The result of this is a high-frequency pulsatory signal at theoutlet of the two ampliers.

The signal which leaves the receiver has a spectrum of equidistant linesor components, the medial line of which is that of the frequency of thereceived carrier wave and the others of which are spaced from thismedial line by multiples of the blocking and unblocking frequency. Eachof these lines is accompanied by lateral lines which correspond to thefrequency of modulation of the signal. The pulsated signal leaving thereceiver is filtered so as to leave only the fundamental component (i.e. the component having the carrier frequency) which is then applied tothe transmitter which it drives.

The signal which leaves the transmitter is radiated and constitutes theretransmitted signal. This retransmitted signal arrives at the receiverduring the blocking times of the latter.

Summarising, the signal to be retransmitted arrives continuously at thereceiver during the periods of blocking and together during the periodsof unblocking of the latter, and this signal becomes a pulsatory signal.The lter extracts from it the fundamental component which is availablewithout interruption at the outlet of the lter and serves for drivingthe transmiten It is to be noted that the circuits of the receiver whichprecede the circuit to which the blocking signal is applied should havea sufficient bandwidth so as not to deform the retransmitted pulsatedsignal. Without this condition, a spectral decomposition of the latterwould take place and the fundamental component, possibly accompanied bysome harmonics, would be present at the inlet of the blocking circuitduring the unblocking time of the latter and would be retransmitted.There would therefore be in this case a singing action. If theselprecautions are taken, the following result is obtained: the fundamentalcomponent of the signal to be retransmitted, which has been madepulsatory by the blocking of the receiver, passes through the filter,whilst the fundamental component of the retransmitted signal, which ispulsatory by nature, does not pass through the filter.

Other objects and features of the invention will appear on reading thefollowing detailed description and examining the accompanying drawings,in which:

Fig. 1 represents the retransmitter of the invention in the form of ablock diagram;

Fig. 2 represents the shape of the signals at different points in thediagram shown in Fig. 1;

Figs. 3 and 3a represent the spectral composition of the signals atdifferent points of the diagram shown in Fig. 1;

Fig. 4 is a detail representation of the quench oscillator of theretransmitter; and

Fig. 5 represents the shape of the signals at different points of theoscillator shown in Fig. 4.

Referring to Fig. 1, 8 is a reception aerial which receives a continuousradio communication of carrier frequency fo having a bandwidth of Afo.The voltage received in the aerial is represented by Fig. 2a. Thisvoltage is applied to the inlet of a radio-frequency reception amplifierhaving a bandwidth of ciF (with k1 considerably greater than 1) which issuiiicient to amplify, without deformation, a pulsatory wave having acarrier frequency of fo and a frequency of recurrence of F for reasonswhich will be hereinafter explained. The amplifier I is unblockedperiodically, at a frequency of F, by application, to one of its stages,of rectangular pulses supplied by the keying oscillator 2. The signalleaving the amplifier I is represented by Fig. 2b. It is composed of avoltwhere m is an integer.

The voltage leaving I is applied to the frequency-converter stage 3which receives, from the local oscillator 4, a voltage of frequency f.The output signal of 3 is a pulsatcry voltage represented in Fig. 2c andhaving the same shape as that of Fig. 2b, but the carrier frequency ofthe signal being, in this case, f-fo.

The voltage leaving 3 is applied to the inlet of a pass-band amplifierfilter 5 having a mean frequency of f--fo and a pass band lcsF which islower than F (k3 is lower than l) so as to allow to pass and to beamplified only the fundamental component of frequent?,7 -o of the signalof Fig. 2c. In addition, this pass band should be greater than or equalto Afo. The signal leaving 5 is represented in Fig. 2d; this is anon-pulsatory voltage of frequency ,f-f0. This signal is brought back tothe frequency fo in the frequency-converter stage 6 which receives asignal of frequency f from the local oscillator 4. There is obtained, atthe outlet of E, the signal represented in Fig. 2e.

The latter signal is applied to a radio-frequency transmitting amplifierI (for example the power amplifier of the retransmitter) This amplifierhas a bandwidth of kzF (with k2 considerably greater than 1) which issufficient for amplifying, without deformation, a pulsatory wave of acarrier frequency of f, and of a repetition frequency of F. It isunblocked periodically, at the same frequency F, by application, to oneof its stages, of rectangular-pulses also supplied by the keyingoscillator 2.

The amplifier 'I is unblocked when the amplifier I is blocked and viceversa. For this purpose, the unblocking pulses II of 'I take placeduring the intervals between the unblocking pulses II) of I. However,the pulses II'I` and II are not exactly opposite in phase and there isleft, between the end of a pulse I0 and the commencement of a pulse II adead period f1, and between the end of a pulse I I and the commencementof a pulse I0 a dead period f2. If 01 and 02 are respectively theduration of a pulse IIJ and the duration of a pulse I I, then Theutility of the dead periods T1 and f2 will be explained hereinafter.

The outlet of the amplifier 'I is connected to the transmitting aerial 9and the signal transmitted by this aerial is represented by Fig. 2f. Itis the same signal as that of Fig. 2b, but the pulses I0 and the pulsesII are interlaced. The result of this is that any reaction between theretransmitted wave and the incident wave is eliminated. In fact, theretransmitted wave (Fig. 2j) is present to the inlet of the amplifier Iduring the periods in which the latter is blocked and, as this amplifierhas a bandwidth of lciF which is considerably greater than F, it doesnot deform the received signal. If, in fact, there had been adeformation, a component of the signal of Fig. 2f, either thefundamental component of frequency fo alone or this fundamentalcomponent accompanied by the rst harmonics of the spectrum (1), would bepresent at the output of the stage of amplifier I preceding that towhich are applied the blocking pulses, together during the blockingperiods and the unblocking periods of the latter and would beretransmitted during the latter periods; there would therefore be, inthis case, coupling between the transmission and the reception.

The wave transmitted by the transmitting aerial 9 is received by thefinal recipient either in the form of pulses of carrier frequency fo or,in a selective receiver, on the fundamental component fo or on one ofthe lines of the spectrum foimF.

In order to x ones ideas and by way of nonlimitative example, let usassume that the radio communication to be received and to beretransmitted has a carrier frequency f=120 mc./s.

and a bandwidth Af0 2 0.25 mc./s.

that is to say, it has a spectrum comprised between 119.75 and 120.25mc./s. Let the keying frequency be F=830 kc./s. The spectrum of the wavetransmitted by the aerial 9 as well as that 4of the output signal yofthe amplifier I are represented by Fig.v 3 inwhich the line I2 ofifre-.quency 120 mc./s. represents the carrier frequency, the lines I3 and I4of frequency 119.75 and 120.25 mc./s. represent the lateral bandsdue tothe modulation of the carrier frequency, the lines I5, I6, I1, I8, I9and 380i frequencies 120.83, 121.66, 122.49, 123.32, 124.15 and 124.98mc./s. .represent the upper lateral bands due to the quenching of thecarrier frequency and the lines 20, 21|, 22, 23, 24 and 39 offrequencies 119.17, 118.34, 117.51, 116.68, 115.85 and 115.02 mc./s.represent the lower lateral bands due to the quenching.

Let us assume, as the bandwidth of the amplifiersI and 1,

that is to say that their pass band will extend vfrom the line 25 offrequency 115 mc./s. to the line 26 of frequency 125 mc./s. Finally-letus assume for the pass band of the amplifier iilter soth'at the limitsof this pass band will be exactly the lines I3 and I4. As it isdiflicult toiilter directly a signal of 120 mc./s. over a bandwidth of0.5 mc./s., its frequency will be reduced to 10 mc./s. by mixing it inthe frequency-converter 3 with a signal of 110 mc./s., then it will befiltered inthe amplifier lter 5 and its original frequency will berestored by mixing it in the frequency 6 with the same signal of 110mc./s.

It has been assumed, in Fig. 3, that the interval between the laterallines I3 and I4 was equal to the bandwith of the lter` In the generalcase, the bandwith of the communication is very much less than thebandwidth of the filter, e. g., 6 kc./s. in relation to 500 kc./s.Consequently, the responder can retransmit simultaneously a plurality ofradio communications, the carrier frequenciesy fo, f'o and the lateralbands of which are represented respectively at I2, 69 and I0-for a rstcommunication and at I2", 35' and for a second communication in Fig. 3a.on the condition that the carrier frequencies such as fu and f'o areinside the pass band of the filter. The possible number ofcommunications retransmitted simultaneously is equal to the ratio ofther bandwidth of the iilter to the bandwidth of Referring to Fig. 4,which represents the .keying oscillator, this oscillator comprises afirst oscillating tube 4I, the oscillating circuit of which is composedof the inductance 42, the xed condenser 43 and the variable condenser44. The sine oscillations of frequency F, which are produced in thefirst Astage and are represented in Fig. 5a, are received at theterminals of the choke coil 45 and applied to the grid 41 of theamplifyingtube 46 and to the. grid of the phase vinverting tube 5I.phase inverting tube 5I is connected to the grid 53 of the amplifyingtube 52.

Amplifying tubes y45 and 52 operate in class C and sine pulses, whichare represented in Figs. 5b and 5c, are produced in their anodecircuits. The

On the other band, the output .of the 6 width 21 ofthe base vof eachsine pulse obtained is less than the half-'period of the base of acomplete sinusoid arch. The width 21 of the base of each pulse isdetermined by regulating, on the one hand, the potential lof the cathode43 of the tube 46 by means of the variable resistor 49 and of thesliding contact 50 connected to the said cathode and, on the other, thepotential of the cathode 54 of the tube 52 by means of the variableresistor 55 and of the sliding contact 56 connected to the lattercathode. Each of the variable resistors 43 and 55 is rconnected betweenearth and the high voltage and, on displacing the sliding contacts and56 to the side of increasing potentials, the polarisation potentials ofthe grids 41 and 53 represented by the lines 23 and 29 of Figs. 5b and5c respectively are separated from the cut-ori voltages of the tubesAfII and 52 represented by the lines 30 and 31| of these figures; theresult of this is to diminish the width 21 of the sine pulses.

These sine pulses of Figs. '5b and 5c are applied respectively to thegrids 58 and 64 of the class-C amplifying tubes 51 and B3. The potentialof the cathode 59 of the tube 51 is regulatable by displacing thesliding contact S0 on the variable resistor ISI. Gn displacing thesliding contact 60 towards the increasing potentials, the line 32 whichclips the pulses of Fig. 5b is approached of the line 33 representingtheir base. Finally, there are obtained, at the terminals of the anoderesistance 32 of the tube 61, the pulses I0 of Fig` 5d which are appliedas unblocking pulses to the amplifier I.

The potential of the cathode 35 of the tube 63 -is regulatable bydisplacing the-sliding contact 53 on the variable resistor B1. Ondisplacing the sliding contact towards the increasingpotentials, theline 33 which clips the pulses of Fig. 5c is approached of the line 3Irepresenting their base. Finally, there are obtained, at the terminalsof the anode resistance 53 of the tube 63, the pulses I I of Fig. 5cwhich are applied as unblocking pulses to the ampliiier 1.

The end 34 of a pulse I3 and the commencement 35 of a pulse I I areseparated by an interval of time of n, and the end 35 of a pulse Il andthe commencement 31 of a pulse I0 are separated by an interval of timeof T2. The receiving amplifier I is unblocked between 31 and 34; duringthe interval n, comprised between 34 and 35, the receiving andtransmitting amplifiers are both blocked; the transmitting ampliner 1 isunblocked between 35 and 35'; during the interval --rz comprised between36 and 31, the two ampliers are both blocked.

The dead period n between the end of the unblocking of the reception andthe lcommencement of the unblocking of the retransmission enables thecircuits of the amplier i to return to the condition of rest, that is tosay to the blocked condition. The dead period r2 between the vend of theunblocking of the retransmission and the commencement of the unblockingof the reception enables the circuits of the amplifier 1 to return tothe condition of rest, that is to say to the blocked condition. Thelatter dead period, in addition, enables the energy which isretransmitted by the aerial 9 and which is reflected by near obstaclesto be present to the input of the amplifier I when the latter is stillblocked. If it is assumed, for example, that the nearest obstacle thatgives harmful refiections is at 50 metres from the aerial 9, thereflected wave requires l -ti 3 10 second to return to the aerial 8which is supposed to be in the immediate vicinity of the aerial 9. Itwill therefore be necessary to have -rz greater than or equal toone-third of a microsecond.

Although certain parts of the invention have been described by way ofexample, the general idea of the invention can be gathered sufiicientlyfrom the foregoing for the person skilled in the art to be able to makenumerous modifications without departing from its scope.

What I claim is:

1. A responder for retransmitting a plurality of incoming continuousmodulated carrier waves of given frequencies applied thereto comprisinginput means for receiving said incoming continuous modulated waves,output retransmitting means driven by said waves, a free running keyingoscillator having two outputs in push-pull relationship respectivelyconnected to the input receiving means and to the output retransmittingmeans and producing on said outputs two blocking signals substantiallyin phase opposition for alternately blocking said input and outputmeans, whereby the output waves of the receiving 'and retransmittingmeans are pulsed at the blocking signal frequency, a pass band filtercoupling the input receiving means to the output retransmitting means,having a narrow bandwidth with respect to the blocking signal frequencyand allowing to pass therethrough the waves driving the retransmittingmeans, the receiving and retransmitting means having a large bandwidthwith respect to the blocking signal frequency, whereby the fundamentalcomponents of the output waves of the receiving means which are derivedfrom the incoming waves continuously present at said receiving meansinput are passed through the filter to drive the output means while thefundamental components of the output waves of the receiving means whichare derived from the retransmitted waves occurring at said receivingmeans input when the same are blocked and are not passed through thefilter.

2. A responder for retransmitting a plurality of incoming continuousmodulated carrier waves of given frequencies applied thereto comprisinga radio-frequency receiving amplifier, a rst frequency converterconnected to said amplifier, a radio-frequency transmitting amplifierdriven by the incoming waves, a second frequency converter connected tosaid latter amplifier, a local oscillator connected to the first andsecond frequency converters, a free running keying oscillator having twooutputs in push-pull relationship respectively connected to theradio-frequency receiving and transmitting amplifiers and producing onsaid outputs two blocking signals substantially in phase opposition foralternately blocking said radio-frequency receiving and transmittingamplifiers whereby the output waves of said both amplifiers are pulsedat the blocking signal frequency, a pass band filter 'coupling the firstand second frequency Vconverters, having a narrow bandwidth with respectto the blocking signal frequency and a1- lowing to pass therethrough theincoming waves being changed in frequency by the first frequencyconverter, the receiving and retransmitting radio-frequency amplifiershaving a large bandwidth with respect to the blocking signal frequency,whereby the fundamental components of the output waves of the receivingamplifier, being changed in frequency by the first frequency converter,which are derived from the incoming waves continuously present at saidreceiving amplifier input are passed through the filter, to be broughtback to their original carrier frequency by the second frequencyconverter and drive the transmitting amplifier while the fundamentalcomponents of the output waves of the receiving amplifier, being changedin frequency by the first frequency converter, which are derived fromthe retransmitted waves occurring at said receiving amplifier input whenthe same is blocked are not passed through the filter.

3. A responder for retransmitting a plurality of incoming continuousmodulated carrier waves of given frequencies applied thereto comprisinginput means for receiving said incoming continuous modulated waves,output retransmitting means driven by said waves, a free-running keyingoscillator having two outputs n push-pull relationship respectivelyconnected to the input receiving means and to the output retransmittingmeans and producing on said outputs a periodic signal which comprises ineach cycle a first period during which the input receiving means areunblocked, a second period during which both the input receiving andoutput retransmitting means are blocked, a third period during which theoutput retransmitting means are unblocked and a fourth period duringwhich both the input receiving and the output retransmitting means areblocked, whereby the output waves of said receiving and retransmittingmeans are pulsed at said signal frequency, a pass band filter couplingthe input receiving means to the output retransmitting means, having anarrow bandwidth with respect to the blocking signal frequency andallowing to pass therethrough the waves driving the retransmittingmeans, the receiving and retransmitting means having a large bandwidthwith respect to the blocking signal frequency, whereby the fundamentalcomponents of the output waves of the receiving means which are derivedfrom the incoming waves continuously present at said receiving meansinput are passed through the filter to drive the output means while thefundamental components of the output waves of the receiving means whichare derived from the retransmitted waves occurring at said receivingmeans input when the same are blocked are not passed through the filter.

PIERRE C. MARCOU.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,425,315 Atwood et al Aug. 12, 1947 2,427,191 Brink Sept. 9,1947 2,477,585 Dodington Aug. 2, 1949

